Pneumatically-activated pumps are known and used for metering a desired amount of a lubricant or other fluid from a source to a tool or machine. One type of pneumatically-activated pump is an air tool lubricator that is used to deliver precise amounts of a lubricant, typically an oil, to an air tool. The air tool lubricator is coupled to an air line upstream from the air tool and senses air flow when the tool is cycled, whereupon the lubricator injects a precise volume of lubricant into the airline. The air stream in the air line then carries the lubricant to the air tool. An example of an air tool lubricator is found in U.S. Pat. No. 4,450,938 (Davenport) which has a single ball check design that deposits oil directly into the air line.
In other lubricators, such as the Servo Meters.TM. lubricator (Master Pneumatic-Detroit, Inc.), air pressure on a piston pushes a metering pin into a bored hole a preset distance which forces the lubricant through a check valve and into a lubricant line. A ball check valve is used at the air tool so that the lubricant line remains filled with lubricant. A drawback of these lubricators is a tendency to entrap air within the device which reduces their precision.
Other pumps, such as the lubricator shown in U.S. Pat. No. 4,784,584 (Gruett), are made with a two-piece piston arrangement composed of a metering piston and an actuating piston that moves in response to air pulses. The dual-piston construction prevents air from being entrapped within the device, providing more accurate metering of liquid to the air tool. However, the two-piece design is relatively complex, and increases the time and precision required to manufacture a lubricator.
Accordingly, it would be desirable to have a pneumatically-activated pump with a relatively simple design, and which is capable of preventing air from being entrapped inside it. It would also be desirable to have a piston for use in a pneumatically-activated lubricator or other pump that is constructed from relatively few components, and is capable of reducing or preventing air entrapment in the pump.